AFM Change

Grumpy · Postby **Grumpy** » Tue Aug 07, 2007 11:39 am

Have read the articles regarding the RX7 AFM swap. Does anyone know if it is possible to use the AFM from an MX6 ??? Looks just like the MX5 unit, only with bigger inlet and outlet. Took the plastic cover off and looks just the same inside as the RX7 one in UA'S post.

StanTheMan · Postby **StanTheMan** » Tue Aug 07, 2007 12:09 pm

grumpy

there is heaps on this.....not the MX6 but certainly for the RX7 conversion.

If I recall correctly. Shithouse Idle. But about 5hp gain over 6000 rpm

there is also some remidies for the crappy idle

Grumpy · Postby **Grumpy** » Tue Aug 07, 2007 12:36 pm

Uncle, I know you have done the conversion. Can you give me the part numbers off the RX7 AFM please ???
It may be the same unit anyway.

Uncle Arthur · Postby **Uncle Arthur** » Tue Aug 07, 2007 2:32 pm

Grumpy wrote:Uncle, I know you have done the conversion. Can you give me the part numbers off the RX7 AFM please ???

I have - but no - I sanded off any hint of part numbers when I polished the unit (and I bought it second hand anyway).

I do believe it's off the atmo RX7, whichever model it is.

The other trick is to swap all your MX5 AFM internals into the RX7 AFM, including the spring. That way you get more flow, but the same voltages and no idle issues.

Grumpy · Postby **Grumpy** » Tue Aug 07, 2007 3:27 pm

Yes, that is what i have been reading/watching on the forum. The part numbers on the MX5 and MX6 units are close, so was just wondering what the RX7 part no was.

Sean · Postby **Sean** » Tue Aug 07, 2007 7:53 pm

Uncle Arthur wrote:
Grumpy wrote:Uncle, I know you have done the conversion. Can you give me the part numbers off the RX7 AFM please ???

I have - but no - I sanded off any hint of part numbers when I polished the unit (and I bought it second hand anyway).

I do believe it's off the atmo RX7, whichever model it is.

The other trick is to swap all your MX5 AFM internals into the RX7 AFM, including the spring. That way you get more flow, but the same voltages and no idle issues.

Wouldn't swapping teh internals give you a lean state?

My reasoning for thinking this are that the mx5 internal think they are flowing 4sq inches when in reality the rx7 body is flowing 5, so the mx5 internals are basically telling teh ecu it's getting less air then it is?

ampz · Postby **ampz** » Tue Aug 07, 2007 8:59 pm

I agree with Sean regarding the extra airflow.
However, the standard mx5 is a drunk anyways, it could do with a little less petrol :mrgreen:

Uncle Arthur · Postby **Uncle Arthur** » Tue Aug 07, 2007 11:47 pm

ampz wrote:I agree with Sean regarding the extra airflow.
However, the standard mx5 is a drunk anyways, it could do with a little less petrol

I also force feed mine :mrgreen:

Matty · Postby **Matty** » Wed Aug 08, 2007 9:08 am

Sean wrote:
Wouldn't swapping teh internals give you a lean state?

My reasoning for thinking this are that the mx5 internal think they are flowing 4sq inches when in reality the rx7 body is flowing 5, so the mx5 internals are basically telling teh ecu it's getting less air then it is?

Yes, it gives you a lean state, but not as badly as an unmodified RX-7 meter, which has an even stiffer spring hence opens less (hence etc....).

You can compensate for the midrange/top end leanness by loosening the spring preload, but then your idle mixture goes to hell.

Ideally you'd need a spring that was even softer than the MX-5's...

adamjp · Postby **adamjp** » Wed Aug 08, 2007 9:12 am

Since converting my MX5 to the RX7 AFM with MX5 internals, my fuel consumption has gone from a steady state 10l/km to 8.9l/km.

So yes, the whole car runs leaner and that is good. My testing when first fitted indicated that at WOT, the car was still rich, even with the additional unannounced air.

If I recall correctly, the B6 MX5 engine ignores the O2 sensor at WOT and only refers to it during cruise. If so, then the cruise condition will sense the additional O2 in the exhaust and add fuel to bring the ratio back to where the ECU thinks it should be.

And as you can see from my measurements, the conversion is much more than just the spring tension. The electrical resistance of the whole system is different too. This alters the voltage reading obtained by the ECU.

Fatty · Postby **Fatty** » Wed Aug 08, 2007 6:30 pm

of course you could use the stock , unmodified mx6 afm in conjunction with a dfa to tune the fuel mixtures however you want them. richer, leaner , whatever you want. i'll be selling my dfa once i get the megasquirt onto the car in the coming months, fyi.